Psych 300A: Midterm 1 Review (Frequency Distributions)

Frequency table

Table that shows the number of individuals located in each category and the scale of measurement

What is the X column on a frequency table

Categories on the IV scale of measurement

What is the f column on a frequency table

Frequency of scores in each category

What does Σf = N tell us

Σ = sum

N = total number of scores

Tells us that the sum of all the frequency scores is equivalent to the total number of scores

What is rf on a frequency table

Relative frequency, fraction of the total group associated with each score

How is rf calculated

rf = f/N

What is cf on a frequency table

It is the cumulative frequency, frequency of scores at or below a particular score

T or F: The cf will always add up to N

T, can only be computed with an interval, ordinal or ratio scale

What is crf on a frequency table

Cumulative relative frequency, proportion of scores at or below a particular score

How is crf calculated

crf = cf/N, can only be computed with ordinal, interval or ratio data

What value should the sum of the crf values add up to

1.000

Grouped frequency table

Scores are grouped together due to there being too many possible rows of data

What are the 5 requirements of a grouped frequency table

1. All intervals are equal width

2. First value in each interval should be a multiple of the width

3. Lowest interval includes the lowest datum value observed

4. Order intervals from lowest to highest

5. List all intervals even when frequency is 0

How does one calculate the number of rows

highest score - lowest score + 1

What happens if a score is between two limits in a grouped frequency table

It shold be grouped due to the real limits

T or F: we can assume data scores from a grouped frequency table

F, we do not know if the lowest value for an interval is actually apart of the data

Stem and leaf display

Way of organizing data that boxes datum in stems and leafs

Stem

leading or significant digit

Leaf

Trailing digit or least significant digit

T or F: Stem and leaf displays need a key

T, tells reader what the categories in the stems represent

T or F: Stem and leaf displays can use all types of scales of measurement

F, must be interval or ratio

What are the 4 types of graphs discussed in this course

1. Bar graph

2. Histogram

3. Polygon

4. Line graph

Bar graph

Used when scale is nominal or ordinal, importantly the bars cannot be touching

Histogram

Used when data is interval or ratio, importantly has no gaps between bars

Polygon

Used when data is interval or ratio, has plotted data points with the shortest root between them drawn, the line must touch f = 0 

Line graph

Used with interval or ratio typically when there are multiple IVs

Shape

Used to describe data, distribution can be symmetrical or skewed

Normal distribution

Also called gaussian distribution, a statistically significant curve that has unique properties

Negative skew

Data is clustered towards the right, tail is on the left

Positive skew

Data is clustered towards the left, tail is on the right

Modality

Number of peaks in a frequency distribution, can be unimodal, bimodal, multimodal or non-modal

Why does a non-modal peak typically occur

When the results are due to random chance

Kurtosis

Degree to which data values are distributed at the tails fo distribution

Platykurtic distribution

Low degree of peakedness, kurtosis is <0

Leptokurtic distribution 

High degree of peakedness, kurtosis >0